[ale] g3 vs g4 vs g5

[D. Alan Stewart]

Graphics cards have nothing to do with Stephen's question! I'm guessing 
that you think the Velocity Engine is part of the graphics hardware. It 
is not. It is an integral part of the G4 and  G5 CPUs.

I'm not a hardware geek, but here's my understanding:

Some history is useful in explaining how the Veolocity Engine relates to 
the G4 and G5 processors. In the old days when you bought a 80x86 
computer typically it had a separate socket on the motherboard that 
could accept a floating point processor chip (FPU). An FPU is a 
specialized processor, it does nothing but floating point math 
calculations, just as graphics boards have specialized processors that 
do nothing but graphics operations. In those days only integer math was 
implemented directly in the CPU hardware. Most people didn't buy one 
because most software in those days made small use of floating point 
math. But if you commonly ran applications that performed a significant 
amount of floating point math (such as CAD or large speadsheets) that 
extra chip was worth the money. However, applications had to be written 
with explicit support for the chip, because the FPU had its own 
intstruction set. If you ran such an application on a computer not 
equipped with an FPU, it would crash. (You could also write programs 
that sensed the presence of the FPU and execute differently based on the 
presence or lack of an FPU or provide software  emulation of the FPU 
when not present.) These days the FPU instruction set is implemented 
directly in 80x86 CPUs.

The Velocity Engine is also a special processer, built into the CPU, 
that performs specialized tasks just as an FPU did. It has its own 
instruction set, just as the FPU did. Programs have to be written 
specifically to recognize and take advantage of  the Velocity Engine. 
(Or use libraries that  implement that behaviour.) The Velocity Engine 
is only useful for certain types of very repetitive and specialized 
tasks. Suitable tasks tend to be performing simple tasks on large input 
data sets that are easily broken into small chunks, such as image 
filters or audio processing.

In summary, the  G3 and G4 chips are 32-bit, but the G4 also has an 
additional, specialized 128-bit Velocity Engine built-in. The G5 is 
64-bit, and like the G4, has a 128-bit Velocity Engine built-in.

Jay Finch wrote:

>The graphics card(s) have nothing to do with the CPU. :~)
>  
>


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